1. Field of the Invention
The invention relates to an accelerometer using an accelerometric sensor having a pendulum structure of the type of those described in U.S. Pat. No. 4,663,972.
According to this patent, U.S. Pat. No. 4,663,972, this pendulum structure is achieved by micro-machining of a substrate consisting in a thin quartz (or any other single crystal) strip and by effecting depositions under vacuum vacuum deposit of suitably arranged conductive surfaces. It comprises a flat moving mass (or test body) suspended on the remaining part of the structure, by means of two parallel thin blades located on both sides of the said mass.
The thickness of these extremely narrow suspension blades is equal to the thickness of the substrate. They enable a translation displacement of the moving mass in a direction parallel to the substrate plane by opposing only a weak elastic return force, so that the sensitive axis of the sensor is located in the substrate plane.
These suspension blades carry conductors which provide an electrical continuity between the metallized areas connected to the moving mass and connecting zones located on the fixed part of the substrate.
This patent further proposes, for the control of the test mass position with respect to the remaining part of the structure, a return motor using the Laplace force obtained by the action of a magnetic induction over a current circulating in at least one coil printed on one of the moving mass faces.
2. Description of the Prior Art
The patent U.S. Pat. No. 4,711,128 filed in the name of the Applicant proposes, for the control of the test mass position with respect to the remaining part of the structure, using of electrostatic forces produced by means of voltages applied to metallic surfaces facing each other.
The specifications of said U.S. patents are incorporated in the present specification by way of reference as essential material thereof. In both cases the S-shaped bending of the two suspending blades in the substrate plane enables a translation movement for the test body, in the direction of the sensitive axis. When the test mass moves away from its equilibrium position, under the effect of the acceleration to be measured, the average direction of the suspending blades is not exactly perpendicular to the initial direction of the sensitive axis.
Therefore, the apparatus is sensitive to the acceleration component which is perpendicular to the initial sensitive axis. In a controlled accelerometer this gives rise, among other effects, to a measurement error known as "vibropendulosity" under dynamic operation. On a non-controlled accelerometer a shifting of the sensitive axis orientation effective with respect to the sensor box is obtained, among other effects.